1. Field of the Invention
This invention relates to rheology modifiers used to adjust the rheological properties of polymeric compositions, and, more particularly, to non-continuous, vinyl lactam polymeric compositions with two-phases therein, having advantageous rheology properties in commercial applications.
2. Description of the Prior Art
Rheology modifiers are used generally to adjust or modify the rheological properties of aqueous compositions. Such properties include, without limitation, viscosity, flow rate, stability to viscosity change over time, and the ability to suspend particles in such aqueous compositions. The particular type of modifier used usually depends on the particular aqueous composition to be modified and on the end-use of the modified aqueous composition. Examples of conventional rheology modifiers include thickeners such as cellulosic derivatives, polyvinyl alcohol, sodium polyacrylate, and other water-soluble macromolecules, and copolymeric emulsions in which monomers with acid groups have been introduced onto the main chain. Such thickeners are used widely in fiber treatment and adhesives.
The rheological properties of concentrated dispersions are critical to many important commercial applications. Examples include coatings, inks, films, oils, paints, food additives and pharmaceuticals. Accordingly, the microscopic and macroscopic dispersion structure and the resulting flow properties of such systems are of both scientific and practical interest. The art has established that sub-micron particles in such systems can have a dramatic effect on the rheology of a polymeric solution or fluid. Several physical critical parameters have been identified as influencing its rheology, including the dispersed particle volume fraction, particle size shape and distribution, the continuous phase viscosity and the fluid flow field. By altering or adjusting these microscopic parameters, certain macroscopic phenomena such as elasticity, shear thinning, thixotropic effect and shear thickening can be modified for a particular application or to exhibit a desired property.
Polymeric compositions of vinyl lactam monomers generally are one-phase, soluble, high viscosity materials. These compositions are useful in a variety of commercial applications such as film formers, dye transfer inhibitors, dispersants, excipients and drug delivery. Aqueous gels of these monomers can also be prepared by light covalent or associative crosslinking of polymer chains resulting in one-phase materials of high viscosity which are effective thickeners in personal care formulations, particularly hair care products.
The prior art in this field is represented by the following patents.
Niessner, in U.S. Pat. Nos. 5,149,750 and 5,180,804, disclosed finely divided, water-swellable gel-like, water-swellable copolymers by polymerization of comonomers in the presence of a surfactant.
Liu, in U.S. Pat. No. 5,997,855, described a homogeneous terpolymer for hair care use, however, without a crosslinking agent.
Kopolow, in U.S. Pat. No. 5,130,121, described personal care compositions containing a stabilized cosmetically-active product obtained by in situ polymerization of a water-soluble vinyl monomer in the presence of discrete microdroplets of a cosmetically-active oil in water.
Blankenburg, in U.S. Pat. Nos. 5,635,169 and 6,107,397, described uncrosslinked aqueous copolymer dispersions of nonionic water-soluble monomers with N-vinyl groups and hydrophobic monomers.
Steckler, in U.S. Pat. No. 3,878,175, disclosed highly absorbent spongy gel polymer materials by simultaneous copolymerization and partial crosslinking of a comonomer mixture of an alkyl acrylate and a heterocyclic N-vinyl monomer containing a carbonyl functionality in the presence of a hydrophobic liquid diluent in which the final polymer is insoluble.
Markus, in U.S. Pat. No. 2,810,716, described a process for making swellable resins by copolymerizing monomers in the presence of a water-soluble non-redox divalent-ion containing salt.
Tseng, in U.S. Pat. Nos. 5,393,854 and 5,717,045, disclosed a one-phase, aqueous gel of crosslinked copolymers of vinyl pyrrolidone and dimethylaminoethyl methacrylate for use in hair care products. The crosslinking agent was 1-vinyl-3-(E)-ethylidene pyrrolidone. The gels had a Brookfield viscosity of between 60,000 and 100,000.
These references illustrate the desire of the art to produce a continuous network of polymer molecules, or microgel, which is a one-phase system, and of high viscosity.
Accordingly, it is an object of this invention to provide a new and improved rheology modifier composition to adjust the rheological properties of commercial products.
A particular object of the present invention is to provide a rheology modifier which is an aqueous polymeric composition of a water-soluble polymer, and including in situ-formed, minute resinous particles dispersed therein, that, under suitable light magnification, shows the presence of two-discrete phases therein, one being the water soluble polymer and the other being water-insoluble resinous particles.